There is an increasing demand for packaged optical fiber devices such as fused-fiber devices whose packaging is more efficient at conducting internally generated heat to the external heat sink, and thus are reliably able to transmit higher optical powers. Both power handling and reliability are generally significantly affected by the packaging of the device. Packaged fused-fiber devices are commonly produced with housings of circular or rectangular profile. Inside the housing is generally a thermally conductive substrate upon which a suitable adhesive (or affixment) material is applied on or proximate to the fused portion on both sides of the fused portion/splice to secure this fiber section to the housing. It is generally within this affixment material that optical loss from the fiber first appears as heat. The substrate conventionally has a D-shaped or slab-shaped geometry, and may have a slotted region in which to locate the fused portion of the device.
During operation of a fused-fiber device, the splice will produce core loss due to optical scattering resulting in some of the light in the fiber core launched (leaking into) into the surrounding cladding which may then be stripped by the affixment material. At high powers this may lead to significant heating of the affixment material. Hence, it may be advantageous to strip this light before it reaches the affixment material. Conventional stripping in a “cladding mode stripper device” for instance (typically a housed double clad fiber (DCF) with its low index polymer (LIP) coating removed) use an adhesive(s) applied onto the cladding of the fiber to strip essentially all pump light cladding modes without perturbing the amplified signal light propagating in the single mode core. As a result, amplified output light from a laser system has an improved M2 because the unwanted multimode light is removed by the adhesive (e.g., an epoxy glue) to the substrate within the package.
In the case of tapered fused bundle (TFB) device the splice between the fused bundle and its output fiber (which can have a glass cladding or a LIP coating thereon) gives rise to high order cladding modes not captured by the core of the output fiber. For the case of a glass clad fused fiber device, in contrast to a LIP fused fiber device, fiber stripping around the splice removes the outer higher index (e.g. acrylate) buffer layer leaving only the glass cladding (e.g., doped silica) on the output fiber proximate to the splice. The adhesive (e.g., a polymer glue) for the glass clad fused fiber device in contrast to the LIP fused fiber device can be placed in direct physical contact with the stripped fiber of the output fiber as this arrangement will not result in a loss of guided mode light within the fiber core because the guided fiber core region is protected from light loss by the glass cladding thereon.